Why in the world would you think that the layers below the flood would form any different then afterwards.
The during the flood part might be kind of complicated though.
What would you expect to be different?
And there are differences.
Be aware the I asked these questions myself.
You may not want to find what you will find.
The best explaination I have heard which explains the iridium layer is a meteor strike.
The Earth went through some geological turmoil and radioactive materials were dispersed on the Earths surface.
The expected results are earthquakes, floods, tidal waves, and atmospheric climatic changes.
Oh, and a lot of dead things all at once.
My personal opnion was developed after looking a the meteor impact distribution at this site.
http://www.unb.ca/passc/ImpactDatabase/CILocSort.html
Notice that the meteor impacts are not random, indicating the concentrated impacts are part of a single event.
The estimated equivalent megaton total from the meteor creator record is about 12,000 times the current nuclear arsenal of the world.
The next question of course is what does an event of this sort do to the slow gradual assumptions normally applied to Earth history theory.
Duane